My Asus TP300LD has a 500GB HDD (https://goo.gl/u6WL6n)
and it seems to be always running at a 100% work load. Also some times the HDD would make a click (like da one u make with ya tongue) occasionally. Is it failing?
Drive clicking is a very immediate indication that your drive is not well. I would suggest backing up all your files and replacing that HDD ASAP.
I have to second this. Looks like your drive is failing and you need to replace it soon. For help with choosing a new drive or the installation of it, just PM me and I can help you out.